S Phylogeny. When did the most recent common ancestor V of two organisms A and B live? In the ‘infinite sites mutation model’, it is assumed that the mutations of a fixed gene occur along the lines of descent from V to A and V to B at the times of independent Poisson processes with known intensity (i.e., mutation rate)  > 0. It is also assumed that each mutation changes a different nucleotide in the gene sequence. Let x be the observed number of nucleotides that differ in the sequences of A and B. What is your maximum likelihood estimate of the age of V ? First specify the statistical model!